Esters of trimethyladipic acid



Patented Apr. 10, 1951 2,548,493 ESTERS F TRIMETHYLADIPIC ACID Richard F. Robey, Cranford, N. .L, assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application August 3, 1948,

. 7 Serial No. 42,329

This invention relates to a new class of compoundswhich have been found'to be particularly suitable for use as synthetic lubricants because of their loW pour points and high viscosity indices.

In the lubricant art, considerable progress has been realized in recent years in the production of lubricants characterized by one or more specific properties and adapted for particular uses. In the main, this progress can be attributed to two developments: the first, new refining procedures, and the second, addition agents capable of imparting particular properties to. available lubricantsJ Thus, viscosity index improvers and pour depressants are added to automotive lubricants to render the lubricants more adaptable to wide changes in temperature conditions, While other agents are added to improve the load carrying properties of a lubricant which is to be employed, for example, under extreme pressure conditions.

Recently, in an efiort to obtain superior lubricants endowed with specific and superior char--' acteristics, a new field has been explored, namely, the synthesis of lubricants from various materials. Esters represent one class of materials which have attracted unusual interest as syn-.- thetic lubricants. In general, they are characterized by higher viscosity indices and lower pour points than mineral oils of corresponding viscosity. The esters described in the present specification have been found to exhibit these desirable characteristics. Lubricants possessing such properties are of special value in the lubrication of engines which are subjected to high temperatures such as combustion turbine engines, particularly those of the prop-jet type. Mineral oil lubricants containing added viscosity index improvers, thickeners or other highly nonvolatile additives are undesirable for use in such engines because of the tendency to leave a' residue which accumulates and interferes with the operation of the engine. A synthetic lubricant of the type described in the present specification is especially adapted to use under such conditions, since the lubricant contains no additives and thus tends to leave no residue upon volatilization.

It has been found that long chain esters of alkylated adipic acids are suitable for use as synthetic lubricants. These include esters of long chain alkylated adipic acids, e. g., octadecyladipic acid. A more preferred group of esters, notable especially for their high viscosity indices and low pour points, are the fully esterified trimethyladipic acids, wherein the esterifying group is an aliphatic hydrocarbon radical of 1 4 Claims. (Cl. 260-485) Y 2 to 18 carbon atoms, chosen so that the total number of carbon atoms in both esterifying groups is 12 to 36. The esterifying groups may be saturated or unsaturated and maybe of a straight chain or branched chain character. The groups Which esterify thetwo carboxyl groups of the acid may be alike or unlike in chain length or other characteristics.

irimethyladipic acid, which undoubtedly consists of a mixture of the two isomeric forms having the structures may be readily prepared by oxidizing dihydroisophorone with nitric acid, a detailed method for carrying out thepreparationbeing described hereinafter. The trimethyladipic acid may be readily esterified by refluxing with a suitable alcohol in the presence of a catalyst such as p-toluenesulfonic acid monohydrate and a suitable medium ior entraining water during the reaction.

Aliphatic alcohols which are suitable for preparing the esters of the present invention include the primary alcohols, saturated and unsaturated, of the C1 to C18 range, e. g., methyl, ethyl, n-propyl, n-butyl, n amyl, n-hexyl, n-octyl, n-decyl, n-dodecyl, n-tetradecyl, cetyl, oleyl and n-octadecyl alcohols, as well as branched chain primary alcohols, e. g., Z-ethylhexyl alcohol. Another group of alcohols especially adapted for use in connection with the present invention are the so called OX0 alcohols, prepared by the reaction of carbon monoxide and hydrogen upon C2 to C17 olefins obtainable from petroleum sources. Materials such as diisobutylene and polypropylene are suitable for this purpose. The alcohols obtained normally have a branched chain structure.

Data will be given below showing properties of a number of examples of esters of trimethyladipic acid, particularly with respect to their usefulness as synthetic lubricating oils. All of the esters were prepared by esterifying trimethyladipic acid, which was prepared by the following method: In an all-glass apparatus, consisting of a 3-liter flask fitted with a stirrer, condenser, and dropping funnel, was placed 1.5

liters (16 mols) of 50% aqueous nitric acid solu tion. This material was heated to boiling and 350 grams (2.5 mols) of dihydroisophorone was point data for the n-dodecyl esters are given in Table II.

added dropwise at such a rate that refluxing Table H continued rapidly. The refluxin was continued for several hours after the addition of the dihy- Acid Alcohol fan; droisophorone was complete. The resulting solution was nearly neutralized with sodium hy- D droxide, and the top layer resulting from this f mf +36 procedure was separated. After washing the Fj -g product three or four times with a saturated @rietfiiahifiu.---- i ZIIIIdg 32 aqueous sodium chloride solution, benzenewas wa em 2 0 i i iig zg ,2 2 3: 2, as: 1%;: g zgg g The esters of the present invention not only Vacuum tripping to We 307 grams of product possess good lubricating qualities in themselves This material may distilled or used in but they may be also blended with mineral lubricrude state eating oils to give lubricants of improved viscos- Each of the esters described in the table below x22: i gg gg g was prepared by esterifying the trimethyladipic acid obtained in the above described process in fl g fi m m matter hilly accordance with the following procedure which es ed yadlplc acld the eggnfymg is perfectly general in its application: A mixture radlcals bemg alkyl radlcals each P m to containing 1 mol of trimethyladipic acid, 2.2 mols carbon i the two estenfyma radicals of alcohol 07% by Weight of p-toluenesulfoni i r conta ning a total of 12 to 06 carbon oms acid monohydrate, and a water entraimng mate- 25 a rial such as benzene, toluene, naphtha, or the A ff P accordmg to clalm m whlqh like, was refluxed until no more water collected i estelfymg radcals are normal Straight cham in the water trap connected to the refluxing cona gsg g i ggsg g grams 23 2 denser. Then the mixture was washed three dengrl g g laldi s er e times with a saturated solution of sodium car- I As a new Com bonate and once with Water. After drying over d 1 t f t th 1 a e a desiccant such as Drierite (anhydrous 0 ecy es el nme iggifi gg CaSOr), the product was stripped at 210-225 C. under 5 mm. pressure. REFEREN The esters obtained by the above typical reacm CBS CITED tion method were found to have the properties lhe following references are of record in the set forth in Table I. file 0f thls Patent Table I Kinematic Viscosity Oflggd Point Alcohol Used in Esterification fggg gig? g z 25%???23? 100 F. 210 F. a 8 5 F. c. C Oxo alcohol froma 01 olefin 13.790 3.198 108 0. 754 -ss -10 09 0x0 alcohol from d obutylcne 22. 710 4.316 no 0. 751 -35 -10 n-Decanol 16. as 3. 78? 154 0. 724 -35 -l0 n-Dodecanolufi 21. 420 4. 752 158 0. 674 5 -l0 1 A well refined, solventextraeted parafiinic type lubricating oil of SAE-2O viscosity grade.

UNITED STATES PATENTS Name Date Finch Aug. 31, 1948 OTHER REFERENCES Beilstein: Handbuch der organischen Chemie (4th ed.), vol. 2, page 715 (1920), vol. 2, Second supplement, page 605.

Number 

1. AS A NEW COMPOSITION OF MATTER A FULLY ESTERIFIED TRIMETHYLADIPIC ACID, THE ESTERIFYING RADICALS BEING ALKYL RADICALS EACH CONTAINING 1 TO 18 CARBON ATOMS, THE TWO ESTERIFYING RADICALS TOGETHER CONTAINING A TOTAL OF 12 TO 36 CARBON ATOMS. 